1. Field of the Invention
The present invention relates to a functional molecule that shows affinity for a target substance and is suitably used in a variety of fields including drugs, drug delivery and biosensors, as well as in controlling of gene expression level, overcoming diseases caused by abnormal genes, elucidation of the function of a protein translated from gene and development of reaction catalysts. More specifically, the present invention related to a functional molecule suitable for the analysis of proteins, a functional molecule synthesizing amidite used for synthesizing the functional molecule, and a target substance analysis method using them.
2. Description of the Related Art
Unraveling of the whole human genome has shifted the focus of interest of scientists and researchers on the analysis of proteins—gene products. It may not be overstating to say that substantial protein analysis can be made possible only when a molecule that shows affinity for a protein of interest has been successfully obtained. A cell, however, contains many different types of proteins, and the amino acid sequence and structure of many of which are still unknown.
The most common technique for obtaining a molecule that shows affinity for a specific protein is to prepare an affinity antibody by utilizing the immune system of animal. However, this technique uses animals and requires a large quantity of proteins, a large number of processes and large costs. Additionally, no affinity antibody may be obtained for specific substances with this technique.
A technique called aptamer method (also referred to as SELEX) that does not rely on any living organism has been proposed to avoid this problem. However, while a molecule obtained by this technique strongly interacts with a specific protein, this technique is not applicable to all proteins. In view of the above-identified circumstances, the inventors of the present invention proposed a modified aptamer method that is established by improving the aptamer method so as to use a modified nucleic acid analogue (see International Publication No. WO2003/078623). However, since the modified aptamer method uses a modified nucleic acid analogue that includes different modified nucleotide units with different substituents, the properties of each of the substituents have to be considered when amplifying a modified nucleic acid analogue showing affinity for a target substance. Thus, it has been difficult to find an excellent PCR condition. Additionally, the above method has a drawback that a modified nucleic acid analogue that tends to be strongly bonded to a target substance is hard to be amplified by PCR. Therefore, there has been a demand to make further improvements on the above method.